The concept of the system for urgent cardiac diagnostics which enables a patient, wherever he may be, to record his ECG himself and send it to his cardiologist in the remote diagnostic center via commercial telecommunication network (cellular or fixed telephone line) is well known. Namely, on the bases of the received ECG and the conversation with the patient, the cardiologist on duty can decide: a) whether an urgent intervention is needed, b) whether the intervention can be performed by the patient himself, or c) whether the patient's state requires urgent medical intervention, and acts accordingly. It is very important that the most critical period, from the occurrence of the first symptoms until the medical treatment, be minimized (Lenfant C. et al.: Considerations for a national heart attack alert program, Clin. Cardiol. 1990 August; 13 (8 Suppl 8): VIII9-11). There is a number of patents and products which, within the said concept of urgent cardiological diagnostics, offer different solutions for recording and transmitting the ECG signal: U.S. Pat. No. 4,889,134 Greenwold, et al., 1989; U.S. Pat. No. 5,226,431 Bible, et al. 1993; U.S. Pat. No. 5,321,618 Gessman, 1994; U.S. Pat. No. 5,966,692 Langer, et al., 1999; PCT WO 01/70105 A2, B. Bojović 2001; “Instant Memory Recorder” of the company TELESCAN MEDICAL SYSTEMS (TELESCAN MEDICAL SYSTEMS 26424 Table Meadow Road, Auburn, Calif. 9560); “CardioCall Event Recorder” by REYNOLDS MEDICAL (REYNOLDS MEDICAL LTD, John Tate Road, Hertford SG13 7NW United Kingdom) and “Heartwiev P-12” by AEROTEL (AEROTEL LTD. 5 Hazoref st. Holon 58856 Israel). The solutions can be divided into three groups:
1) The first group comprises solutions for sending the recording of one or two standard ECG leads. The mobile recorders of this group can be very small and with integrated electrodes (no cables are needed), which is the advantage of the group. The recording is performed by simple holding of the device on the patient's chest or by positioning the fingers on the integrated electrodes. This is a quick and simple way for a patient to record one or two leads of his ECG. However, recording one or two ECG signals limits the application of these devices to the patients with rhythm disorders, which is about 20% of the patient population with heart diseases. Typical device of this group is “CardioCall Event Recorder” by REYNOLDS MEDICAL.
2) The second group consists of solutions that enable direct recording and transmission of standard 12-lead ECG, thus including their application to the patients with the diagnoses of coronary artery diseases. Namely, in such patients, the complete standard 12-lead ECG is necessary for urgent diagnostics. Some of these devices are equipped with the full set of electrodes and cables for recording all 12 standard ECG leads (usually 10 electrodes, that is cables), which a patient himself attaches onto his body during recording. The typical representative of this group is “12 Lead Memory ECG Recorder” by TELESCAN MEDICAL SYSTEMS. The other method is the use of a reduced number of electrodes that are moved during the recording. For example, if four electrodes are used, three are positioned at the locations of standard ECG leads I, II, and III (arms and legs of the patient), while the fourth electrode has to be moved during recording to each of the six chest positions for recording chest leads V1-V6 (U.S. Pat. No. 4,889,134, Greenwold et al., 1989). The method that uses three cable connected electrodes and four button-shaped integrated electrodes can be found in the device “Heartwiev P-12” by AEROTEL. The recording of 12 leads is performed in three steps: leads D1, D2, D3, aVR, aVL, aVF, V1, and V2 are recorded in the first step, V3 and V4 in the second, and V5 and V6 in the third step. The common disadvantage of the whole group is rather complicated and long-lasting recording procedure, which makes them very inconvenient for self-application, especially for the patients suffering a heart attack. Significant errors are also possible to occur due to the imprecise positioning of the electrodes.
3) The third group includes the solutions in which reduced number of special leads is recorded, and later, on the basis of this recording, all 12 standard ECG leads are reconstructed computationally. The method for the reconstruction of 12 standard ECG leads and/or x,y,z leads of a vectorcardiogram based on the recorded special leads obtained with four electrodes is explained in U.S. Pat. No. 4,850,370, G. E. Dower 1989. The method is based on the dipole approximation of the electrical heart activity and uses the universal transformation matrix T, with dimensions 3×12, and with the matrix coefficients determined experimentally.
The conventional ECG leads (D1, D2, D3, aVR, aVL, aVF, V1, V2, V3, V4, V5, V6) are obtained by multiplying the transformation matrix T with the recorded signals at the special leads s(Vs1, Vs2, Vs3). The universal transformation matrix for all patients does not contain information about individual characteristics of a patient, which results in major errors in the reconstruction of the standard ECG lead signals.
An improvement of this method by introducing the individual transformation matrix is given in the paper by Scherer, J. A. et al., Journal of Electrocardiology, v 22 Suppl, pp. 128, 1989, and applied in the U.S. Pat. No. 5,058,598 (J. M. Niklas et al., 1993), where the implementation of the individual transformation matrix for each patient, with the segment calculation of the transformation matrix coefficients, was suggested (ECG signal is divided into segments and the coefficients for each segment are calculated individually). The reconstruction of the standard ECG lead signals by the individual transformation matrix means that it is necessary to perform the basic (calibrating) recording for each patient, which will be used for the matrix coefficient calculation. The errors in this approach are significantly reduced compared to the method using the universal transformation matrix. The major drawback of both said methods is the need to use cables for recording with the suggested arrangement of electrodes which is very inconvenient for self-application, especially in the patients suffering a heart attack. The method in which the reconstruction of standard ECG leads is also done with the individual transformation matrix (Scherer, J. A. et al., Journal of Electrocardiology, v 22 Suppl, pp. 128, 1989), but with the mobile ECG device with integrated electrodes, i.e. with no cables used, is presented in the patent PCT WO 01/70105 A2, B. Bojović 2001. The device enables quick and easy recording of the special ECG leads and reconstruction of all 12 standard ECG leads with the individual transformation matrix. However, the limitations in the arrangement of the electrodes, due to the use of the integrated ones, disable the optimal arrangement of electrodes on the patient's body, which results in significant errors in the signal reconstruction.
An additional problem present in all three groups is the occurrence of the base line wandering of the ECG signal during recording. The effect is especially undesirable for the third group of the said devices because the base line wandering during the recording of special leads brings about major diagnostic errors in the procedure of the reconstruction of 12 standard ECG leads.